One conventional optical bistable device is described on pages 13 to 15 of "Applied Physics Letters 45(1), 1 July 1984". The optical bistable device is called a self-electro-optic effect device (simply called "SEED" hereinafter) and comprises a multiple quantum well between two intrinsic regions, and p- and n-semiconductor layers provided respectively outside the two intrinsic regions.
In operation, a reverse-biased voltage is applied across the SEED from a power source having a series resistance while a predetermined power of incident light is input thereto whereby the light is absorbed in the multiple quantum well so that photocurrent is induced therein. The incident light wavelength is chosen to be a wavelength at which the exciton resonance peak is produced at nearly zero biased voltage applied across the SEED. Where the power of the incident light is increased, the photocurrent increases, thereby reducing the reverse-biased voltage applied thereacross due to the voltage drop by the series resistance. The thus reduced voltage shifts the exciton resonance peak in the direction of shorter wavelength to result in a further increase of the photocurrent.
Finally, the reverse biased voltage is dropped nearly down to zero so that much of the absorption of the incident light is due to the exciton resonance peak. For this reason, an optical bistability is obtained in the SEED by increasing and decreasing the incident light power. The phenomenon mentioned here will be described in detail later.
In the conventional SEED, however, if the power of the incident light is very small, the induced photocurrent is correspondingly small so that the voltage drop across the series resistance of the power source is very small. For this reason, it is difficult to drop the voltage applied across the SEED nearly down to zero.
If the series resistance is made to be bigger in its value, for the purpose of decreasing the biased voltage nearly down to zero, the response speed becomes lower due to the increase of time constant CR.